"Roy Lewallen" wrote in message
...
Jerry Martes wrote:

I'd submit that, in a practical situation, the mismatch of an antenna
for
receiving can be as high as 2:1 or even 3:1 without degrading the
strength
of the received signal when the transmission line losses are low. I
thought that, if the receiver is tuneable, the actual impedance the
transmission line presents to the receiver can be 'accounted for. I
thought that, for a given antenna and transmission line, the effects of
VSWR
are less important that for delivering power by a transmitter.
Am I wrong when I consider VSWR to be less important for receivers
than
for transmitters?

Jerry

It sounds like you (and some other posters) might be confusing the
transmission line SWR with the impedance seen by the
transmitter/receiver, which is often indicated with an SWR meter. The
two aren't the same.

Consider, for example, a 50 ohm antenna and 50 ohm tx/rx, with a 300 ohm
half wavelength transmission line connecting the two. The antenna sees a
perfect match (50 ohms) when receiving, and the transmitter sees a
perfect match (50 ohms) when transmitting. The transmission line SWR is
6:1 when transmitting and receiving. On the other hand, if the antenna
and transmission line are both 300 ohms (+ j0), the line SWR will be 1:1
when transmitting, 6:1 when receiving. And so forth.

The effects of impedance mismatch seen by the transmitter when
transmitting, the impedance mismatch seen by the antenna when receiving,
and the transmission line SWR are three separate issues. Each has its
own effect on system performance, and each needs to be treated
separately. The importance of one or the other depends on the individual
situation.

Roy Lewallen, W7EL

Roy

It might be that I'm wrong with my conclusion that when receiving, the
loss of received signal wont be appreciably worsened by VSWRs as high as,
say, 3:1, when the line atenuation is under a couple DB. But I dont think
I've been confused about the Line to Load Mismatch and VSWR.

I recognize that the lowest VSWR and lowest line loss and the lowest noise
figure are all important.

Since I'm always working with systems that arent perfect, I dont get
concerned with low VSWR when working with receivers except when there is
need for phasing arrays. It is my understanding that the transmission line
loss isnt increased excessively when the line loss is under about 2 DB and
the VSWR is as high as 3:1, and that S-meter readings arent measureably
degraded when the receiver sees these signals thats not coming in with a 50
ohm internal impedance.

It occurred to me that the original poster of this "Phasing Harness" might
have some sophisticated need for phase or low mismatch. If the two antennas
being harnessed are only to maximize radiation toward the horizon, I'd
consider the question a simple one to answer. ie Feed them in phase with
any convenient equal lengths of line. If bandwidth is a factor, expect
sidelobes to vary with frequency.

But, my knowledge and experience is very limited, so any 'redirection' of
my thinking is appreciated.

Jerry